Touch display apparatuses are easily to operate, so that in recent years the touch display apparatuses have been widely used in many electronic products such as mobile phones, personal digital assistants (PDA), digital cameras, music players, computers, satellite navigation devices and so on.
According to sensing theory, touch display apparatuses can be divided into many types such as resistive type, capacitive type and optical type. In a conventional optical touch display apparatus, a frame made of reflecting material, light-emitting material or light guide material is added to surround display area to emit background light. Thus, the said conventional optical touch display apparatus can calculate the position of a pointer related to the display area according to the shade position of the pointer related to the background light.
However, since the mechanical flatness of the frame is not good or the frame is bended, the conventional optical touch display apparatuses may have a problem of misjudging the position of the pointer.